Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$104.78	11.374%	$116.6977	$116.70	$116.70	$116.70
Purchase #2	$229.55	13.516%	$260.576	$260.58	$260.60	$260.60
Purchase #3	$20.59	3.338%	$21.2773	$21.28	$21.30	$21.30
Purchase #4	$169.71	8.484%	$184.1082	$184.11	$184.10	$184.10
Purchase #5	$73.51	12.167%	$82.454	$82.45	$82.45	$82.50
Purchase #6	$115.61	10.214%	$127.4184	$127.42	$127.40	$127.40
Purchase #7	$5.38	12.677%	$6.062	$6.06	$6.05	$6.10
7 purchase totals =	$719.13		$798.5936	$798.60	$798.60	$798.70